Vibration damper



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Filed April 9, 1926 Fig.1.

Inventor: Edward W Kellogg,

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UNITED STATES PATENT OFFICE.

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vmn'n'rron DAMPER.

Application filed April 9,

My invention relates to vibration dampers. Although not limited thereto, the invention is particularly useful for dampinfg the vibrations and thereby reducing the e fects of resonance in delicate instruments,

-such as telephonic apparatus and other deabsorbent medium. However, it is prefer able to have the absorbent material fully saturated by a viscous liquid. My invention may be compared to a dash-pot. The function of a dash-pot is to resistrapid'motion and absorb mechanical energy. Owing to the mass and flexibility of its parts, however, a dash-pot does not function well where Y the direction of motion reverses nany times per second. For this purpose it is important to eliminate all rods or linkages between the vibrating body and the damping fluid, and to make it possible to absorb a large amount of energy with a very small movement of the liquid, in order that the inertia of the moving liquid may have ne ligible effect. This greatly increased absorpt1on is obtained in my invention by. causing the flow to take place through many minute passages. The absorbent material also serves to hold the liqluid in place, making it unnecessary to provi e any tight container or to maintain the device to which it is applied in any particular upright position. v

'The features of my invention which are believed to be novel and patentable will be ointed out in the claims appended hereto.

' or a better understanding of the invention, reference is made in the following description to the accompanying drawing which shows in Fig. 1 the application of my invention to an electromagnetic cutter used in cuttingthe wax master plate-for producin photograph records; Fig. 2 shows a cro Fig. 3 illustrates the application of the invention to a telephone instrument; and Fig. 4 shows its use with a loud speaker.

In Fig. 1, 10 represents a wax disc supported upon a turntable 11. 12 represents a cutting point by means of which a sound sectional view of the cutter of Fig. 1;.

1926. Serial No. 101,008.

responsive record is cut in the wax disc. The mechanism for rotating the turntable and movm made 1s not shown since it constitutes no part of my invention. 13 is an electromagnetic device for vibrating thecutter in response to analternatin current having a frequency and magnitu e correspondin to the pitch and volume ofthe sound whi i it 1s desired to reproduce. This device has a permanent magnet 14 provided with inwardly projecting pole pieces 15 for producing a concentrated unidirectional flux across the air gap between them. A coil 16 through which the sound responsive alternating current is conducted is provided adjacent the air gap. A'magnetic armature 17 which carries the cutter 12 at its lower en is ivoted at 18 in suitable knife-ed e bearmgs and passes up through coil 16 am? terminates in a flat portion 19 centrally located in the the cutter radially as the record is air gap between the pole pieces15. Threads held in tension by springs, one of which is represented at 20, securely hold the armature knife edges in their grooves while allowing the armature to vibrate in response to the signalling current in coil 16. The alternating current in coil 16 causes the armature to become alternately magnetized. The alternately magnetized armature reacts with the unidirectional field produced by the permanent magnet and moves back and forth accordingly, and its rotation about the pivot axis 18 vibrates the cutter 12 to Produce the desired record.

The frequency of the current in coil 16 varies over a considerable range corresponding to the audible frequencies which it is desiredto reproduce, for example from below 100 cycles to above 4000 cycles per second. The magnitude of this current also varies with the magnitude of sound which it is desired to reproduce. The problem is to cause the mechanical vibrations of the cutter toreproduce faithfully the electrical vibrations, the desired relation for phonograph recording being that at each mstant the velocity of the cutting point shall be proportional to current through the coil. To accomplish this object the moving element comprising the cutter and the armature must be heavily damped. The damping must be reatly in excessof what is generally termed critical damping. A resonant system is critically damped when the resist! ance factor or damping is twice the reactive force of acceleration or elasticity of the vibrating element at the natural. frequency of oscillation. However, in certain acoustic devices such as phonograph record cutters, or electromagnetic telephone transmitters, the damping force, which is proportional to velocity and opposes motion, .must exceed the accelerating force at the highest frequency in the acoustic range and exceed the elastic restoring force at the lowest acoustic frequency.

I In accordance with my invention, I provide a damper 21 comprising a flexible absorbent material, such as felt, substantially saturated with a liquid, such as oil, or glycerine. In the device of Fig. 1 this dam er comprises a pair of felt pads saturated with oil placed on either side of the armature 19 between the armature and the adjacent pole pieces. If the felt pads are left dry they act much like feebly damped springs, so that at some frequency resonance occurs, and at this frequency the response of the device is much greater than at other frequencies. However, when these felt pads are saturated with a liquid, such as machine .oil, the resonant effects disappear, the damping having been so increased that the cutter gives a practically uniform response between vibration frequencies of 100 and 4000 cycles per second. By'uniform response in this instance I mean that for a given input current, the velocity of the moving element in the device is the same at all frequencies within the working range. The damping property of the saturated felt is due to the fact that the liquid is forced from one place to another in the absorbent material through a plurality of short minute capillary passages. This causes a resistance of a type characteristic of viscous flow which is that the force opposing motion is proportional to the velocity of motion. Felt has been mentioned as the absorbent material but this is not essential since any flexible porous material having absorbent properties will serve the purpose. The liquid should be one which will not injure or rust the parts with which it comes in contact and one which will not dry up or gum quickly. I have found ordinary machine oil suitable for most purposes. The felt will hold oil for long periods of time and no specialprovision for supplying the oil is necessary. Where the surface presented by the vibrat ing element to the damping pads is large, it may be desirable to perforate the vibrating member so that the liquid may pass from one side to the other as the member vibrates, or else to provide relief pockets or passages into which the liquid can flow when' the pad is compressed. One such perforation is shown in the armature in Fig. 2 for the purpose of illustration; In general such open ings are not essential in the armature of this particular device, since the contact area. is small and the oil can escape at the edges of the pad. 1

In Fig. 3 I have represented a telephone instrument in which a liquid saturated orous material represented at 21 is provided between the vibratory magnetic diaphragm 22 and the ear piece 23. I have found that the damping improves the quality of reprowhen it is used as a transmitter than when used as a receiver. The presence of the little pads of oiled felt 21 greatly improves the quality of transmitted currents, eliminating resonance, and giving the device a practically uniform response over a wide range of 5 frequencies. In the electromagnetic telephone transmitter the output voltage is proportional to diaphragm velocity, and in order that diaphragm velocity may be proportional to the air pressure in the sound waves for all acoustically important free quencies, the diaphragm must be damped to the same degree as was explained to be necessary for the phonograph record cutter.

Fig. 4 shows the construction of a. loud speaker where oiled felt 21 is placed between a support 24 and the diaphragm 25 to reduce the diaphragm resonance.

While I have particularly explained my invention in connection with acoustic de- 1 vices, other applications of the invention may be useful where it is desired to elimi nate or reduce undesirable vibrations, or to reduce the communication of vibrations from one body to another. It is frequently found that ordinary cushion supports, or alternate cushions and weights, do not completely prevent the transmission of vibrations, but that the use of cushions which are effective absorbers of energy is of great advantage. In

view of this and other useful applications, I do not wish to limit my invention to the particular devices illustrated.

In accordance with the provisions of the patent statutes I have described the prlnciple of operation of my invention, together with the apparatus which I'now consider to represent the most important applications thereof, but I desire to have it understood that the apparatus shown and described is only illustrative and that the invention may be carried out by other means.

lVhat I claim as new and desire to secure by Letters Patent of the United States is:

1. A vibration damper comprising a exible absorbent material containing a liquid.

2. A vibration damper comprising a flexible absorbent material substantially saturated with oil.

3. A vibration damper for acoustic apparatus comprising a flexible porous material substantially saturated with aviscous liquid.

4. In combination, a vibratory member, a stationary supporting member, and damping means for said vibratory member comprising a flexible absorbent material containing a liquid interposed between said vibratory member and said supporting member.

5. A .device subject to vibration over a wide range of frequencies and means for damping such vibrations comprising a flexible absorbent material substantia ly saturated with .a liquid, said material being so placed with reference to the vibrating member, that vibrations will cause movements of the liquid within the absorbent material.

6. An acoustic device subject to electromagnetic vibrations over a wide range of frequencies within the acoustic frequency range, and means for damping said vibrations comprising a flexible absorbent material substantially saturated with a viscous oil and placed in contact with the vibrating parts and in the path of vibratory movement of said acoustic device.

7. An electromagnetic acoustic device comprising a permanent magnet having inwardly projecting-pole pieces separated by a narrow air gap, a magnetic armature member movably supported in said air gap, a coil for alternately magnetizing said armature at'varying frequencies within the acoustic frequency range, reproducing means secured to said armature member, and damping means for said acoustic member com rising pads of porous material substantially saturated with a viscous liquid inserted in said air gap on opposite sides of said armature.

8. The method of damping undesirable vibrations which consists in causing the. vibrating forces to be partially absorbed in forcing liquid through a plurality of minute capillary spaces.

9. A device for cutting phonograph records comprising a cutting stylus, means for vibrating said stylus to produce the record cutting movements and damping means for said cutting stylus comprismg porous flexible material substantially saturated with a liquid.

In witness whereof, I have hereunto set my hand this 7th day of April, 1926.

EDWARD W. KELLOGG. 

